1. Field of the Invention
This invention relates to an improved process for continuously producing catalyzed melt polymerization polymers and apparatus for intimately mixing the components during the process. In particular, this invention relates to the continuous catalytic polymerization of poly(hydroxy acids) using a counter-current impeller mixing system.
2. Description of the Related Art
Poly(hydroxy acids), such as poly(lactic acid) and poly(glycolic acid), are generally known in the art. Conventionally, they have been produced by batchwise polymerization in a heated vessel. The reaction is catalyzed by a number of conventional catalysts: for example see U.S. Pat. Nos. 5,028,667 and 3,839,297.
Continuous catalytic production of polymerized dimers of glycolic and related acids has also been carried out using a heated extrusion screw reactor (see German DE 3936188 A1). While the extrusion screw technique has advantages inherent in a continuous operation, it is costly equipment that is expensive to operate and requires frequent maintenance.
Continuous catalytic polymerization tubular reactors having several sections are also known in the art for the preparation of other polymers, (see U.S. Pat. Nos. 4,948,847 and 4,952,627). Only the aforementioned German DE 3936188 A1 discloses continuous polymerization of a dimer of an alpha-hydroxycarboxylic acid, and as aforementioned, the process therein described is expensive, greatly limiting the economical uses of the polymers made thereby.